Deterioration mechanism of hydrothermal aging on the properties of carbon fiber/epoxy composites in various media

Abstract

This study examined the hydrothermal aging mechanism of carbon fiber reinforced epoxy resin (CF/EP) composites in acidic, alkaline, salt solution, and deionized water (marked as Ac-CF/EP, Al-CF/EP, Sa-CF/EP, and De-CF/EP). The water absorption of carbon fiber reinforced epoxy resin composites followed a two-step process for all four aging mediums, including an initial Fickian diffusion and a subsequent long-term deterioration response. The carbon fiber reinforced epoxy resin composites were degraded more easily in a weak acidic solution due to the degradation of secondary amines and ether bond in an EP molecular chain, which was even degraded into methyl, ethyl, isopropyl, and bisphenol-A monomers. Long-term hydrothermal aging led to significant degradation of the CF/EP composites in all four mediums, the shear strength of the aged composites from small to large was Ac-CF/EP < Al-CF/EP < De-CF/EP < Sa-CF/EP < raw carbon fiber reinforced epoxy resin, which reduced the bending strength by 38.1%, 31.0%, 20.9%, and 11.5%, respectively, compared to the raw carbon fiber reinforced epoxy resin composites. The degradation of the EP matrix and irreversible interface damage caused by hydrothermal aging were considered the main reasons for the degraded mechanical properties of the carbon fiber reinforced epoxy resin composites. It is strongly recommended to apply a protective film on the surface of carbon fiber reinforced epoxy resin composites to reduce the possibility of interaction with humid air.

A review of the effect of hydrothermal aging on the mechanical properties of 2D fiber‐reinforced resin matrix composites

“…For 2D FRRMC Based on the literature, it can be assumed that temperatures greater than 50 C are considered high temperatures 84 for 2D FRRMC, while temperatures ranging from 23 to 25 C are considered room temperature, 85 and temperatures less than À50 C are classified as low temperature. 86 Behera et al 71 Consequently, even if all the solutions in aged CF/EP composites were discharged (Figure 7D), the interfacial strength in the aged CF/EP composites is still degraded substantially, which makes the mechanical properties of the aged composites irreversibly reduced. This suggests that the surfaces of CF/EP composites must be coated with a skin to decrease the interactions with humid air before being placed into service, extending the service life of CF/EP composites.…”

“…For 2D FRRMC Based on the literature, it can be assumed that temperatures greater than 50°C are considered high temperatures 84 for 2D FRRMC, while temperatures ranging from 23 to 25°C are considered room temperature, 85 and temperatures less than −50°C are classified as low temperature 86 . Behera et al 71 studied the effect of static mechanical properties of CFRP multidirectional laminates aged in water at 70°C and room temperature.…”

“…Similarly, Guo et al 86 studied the aging mechanism of carbon fiber‐reinforced epoxy resin (CF/EP) composites. The composites were tested in acidic, alkaline, salt solutions and deionized water (Ac‐CF/EP, Al‐CF/EP, Sa‐CF/EP, and De‐CF/EP) at a high temperature of 50°C.…”

The influence of hygrothermal aging on the hoop tensile strength of glass fiber wound polymer composites fabricated via filament winding technique

“…In harsh environments, the mechanical properties of FRP composites deteriorate as the working temperature rises between 70-80 °C. The aging period, chemical treatment (such as exposure to the sea and distilled water), and working temperature have all been shown to influence the overall strength of FRP composites [38][39][40][41][42]. Recent research has shown that moisture influences matrix osmotic cracking due to the expansion of the gap between fiber and matrix, as well as the debonding of fiber and matrix.…”